How to evaluate dirac function for Infi

2019 3 5
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更新时间：2019 3 5
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dk= 1;
k = -10:dk:10;
G=(dirac(k+8)-2*dirac(k+4)+dirac(k)-2*dirac(k-4)+dirac(k-8)).*exp(-1i*pi.*k/8);
idx = G == Inf; %find Inf
G(idx) = 1; %sets Inf = 1
mag=abs(G);
stem(k,mag)
title('Magnitude vs k')
xlabel('k')
ylabel('Magnitude')
figure
phase=angle(G);
stem(k,phase)
title('Phase vs. k')
xlabel('k')
ylabel('Phase')
I know how to show values when G is equal to Inf, but my issue rises when G = Inf + Infi for example.
I have tried:
idi = G == -Inf + Infi;
G(idi) = 1i;
But no luck. Any help appreciated.

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Walter Roberson
Walter Roberson 2019-3-5

1 个投票

idi = G == complex(-inf, inf);
G(idi) = 1i;

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Elijah Kornefel
Elijah Kornefel 2019-3-5
Thank you, Walter.
Here is the full code to catch every case of infinity:
%% Problem 3_28_b
dk= 1;
k = -10:dk:10;
G=(dirac(k+8)-2*dirac(k+4)+dirac(k)-2*dirac(k-4)+dirac(k-8)).*exp(-1i*pi.*k/8);
idx = G == Inf; %find Inf
idy = G == -Inf; %find -Inf
idi = G == complex(-inf, inf); %find -Inf + Infi
idj = G == complex(-inf, -inf); %find -Inf -Infi
G(idx) = 1;
G(idy) = -1;
G(idi) = -1+1i;
G(idj) = -1-1i;
mag=abs(G);
stem(k,mag)
title('Magnitude vs k')
xlabel('k')
ylabel('Magnitude')
figure
phase=angle(G);
stem(k,phase)
title('Phase vs. k')
xlabel('k')
ylabel('Phase')
Walter Roberson
Walter Roberson 2019-3-5
Could you confirm that your system cannot produce +inf +inf*i ?
You can make the code more compact:
notfin = ~isfinite(G);
G(notfin) = complex(sign(real(G(notfin))), sign(imag(G(notfin))));
Elijah Kornefel
Elijah Kornefel 2019-3-5
This also works. Thank you. I'll be sure to check for these any time I use dirac. My function did not necessarily produce every inf and infi combination, but it is more to check for all. This shorter snippet does that.
Thank you.

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